Cyclic process for the production of methyl methacrylate



United States Patent Ofilice 3,419,601 Patented Dec. 31, 1968 3,419,601 CYCLIC PROCESS FOR THE PRODUCTION OF METHYL METHACRYLATE Charles Levi Isbell, Jr., Charleston, W. Va., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Mar. 3, 1964, Ser. No. 349,536 4 Claims. (Cl. 260-486) ABSTRACT OF THE DISCLOSURE Methyl methacrylate is produced by a cyclic process in which oleum, methanol and acetone cyanohydrin are reacted to form a mixture containing methyl methacrylate and ammonium sulfate; the methyl methacrylate is separated from the mixture and the ammonium sulfate portion is burned to form a gas containing sulfur dioxide which is oxidized to sulfur trioxide and is absorbed with concentrated sulfuric acid before being recycled back to the reaction mixture of ammonium sulfate and methanol.

This invention relates to a cyclic process for the production of methyl methacrylate by the reaction of acetone cyanohydrin with sulfuric acid and methanol in which sulfuric acid is regenerated from a waste stream containing ammonium sulfate and recycled for reaction with additional acetone cyanohydrin.

It is known in the art to produce methyl methacrylate from acetone cyanohydrin by reacting acetone cyanohydrin with fuming sulfuric acid and methanol. See US. Patents 2,042,458, issued June 2, 1936 to Crawford and 2,416,756, issued Mar. 7, 1947 to Jilk. By-products of this reaction include ammonium sulfate and ammonium hydrogen sulfate. These lay-products have only limited commercial value as obtained, and present a disposal problem which adversely affects economics of the overall process. Thus, the by-products of this process have not been desirable. Ammonium sulfate has not been acceptable as a raw material for the production of sulfuric acid because the ammonium tends to recombine with the sulfate resulting in low yields of S Furthermore, the ammonium sulfate tends to form nitric oxides and these products are absorbed during the absorption of 80;, thus resulting in an impure product.

It is an object of this invention to provide a process for the production of methyl methacrylate in which the sulfuric acid is regenerated and again reacted with acetone cyanohydrin. It is a further object of this invention to provide a process for the production of methyl methacrylate without formation of pollution forming by-products. It is a further object of this invention to provide a use for sulfuric acid containing small amounts of nitric acid. It is a further object of this invention to provide a process for the production of sulfuric acid from ammonium sulfate containing materials in which the sulfuric acid is recovered at high yields. Other objects will be apparent to one skilled in the art from the remainder of the specification.

The above objects are accomplished and the above difficulties are overcome according to the present invention by reacting substantially pure acetone cyanohydrin with sulfuric acid, which reaction includes the formation of methacrylamide sulfate according to the following The reaction product is then reacted with methanol and water which reaction includes the formation of methyl methacrylate according to the following equation:

Other compounds present in the resulting mixture include H2804, Water, C3H4O(NH4SO3)2 and 01" ganics having the empirical formula C H O The methyl methacrylate is then separated from the mixture by distillation, and the ammonium hydrogen sulfate containing portion is burned. The products resulting from the burning include CO 0 H O, S0 N oxides of nitrogen, and S0 This efiluent gas is then dried, heated and then passed over a catalyst in the presence of added amounts of oxygen. The S0 is oxidized to S0 and the S0 is removed from the gas by absorption with concentrated sulfuric acid forming fuming sulfuric acid (oleum). This absorption may take place using various techniques, such as a surface-type absorber in which the gas containing the S0 is passed countercurrently over the surface of a stream of concentrated sulfuric acid, or using a bubbling type absorber in which the gas containing is bubbled through concentrated sulfuric acid, or using a packed absorption tower in which the gas containing the S0 is passed up through an absorption tower and concentrated sulfuric acid is passed down through the absorption tower. The concentration of the fuming sulfuric acid is then adjusted to form 6% fuming sulfuric acid, and the 6% fuming sulfuric acid is reacted with additional acetone cyanohydrin.

The burning of the ammonium. sulfate containing mixture must be controlled within a relatively narrow range in order to assure a high yield of sulfuric acid. Specifically, the temperature must be within the range of 850 C. to 1150 C., preferably 950 C. to 1050 C. The reaction of ammonium sulfate is thought to be essentially thermal cracking, and at this temperature the formation of S0 is favored. In a preferred embodiment, the mixture is sprayed into a furnace and burned to form S0 The furnace may be fired with carbon, as in coal, or hydrocarbon gas, such as natural gas; in any event, the resulting product includes CO and C0 The burning of the ammonium sulfate results in the oxidation of the ammonium ion, NHJ, to N and oxides of nitrogen. When operating under the preferred conditions of the process, the greatest portion of the nitrogen is present as N which is not readily oxidized in the oxidation of S0 to S0 and is thus ultimately vented as N After the ammonium sulfate containing mixture has been burned to form a gaseous mixture containing S0 the gaseous mixture is cooled sufficiently to condense most of the water (usually less than 40 (1.), and scrubbed to remove the Water, undecomposed sulfuric acid and ash, heated to between 300 and 500 C., and is then passed over a catalyst. Platinum containing catalysts are operative, but vanadium containing catalysts are preferred since they are less readily poisoned, and because they are not as reactive with nitrogen and thus minimize the amount of N that is oxidized. The oxidation of S0 to S0 is preferably carried out by passing the gas through a catalyst bed at a temperature of about 400 to 600 C. The formation of S0 from S0 is exothermic, and a suitable heat exchange unit can be employed using this heat of reaction to preheat the incoming gas; of course, the heat can be supplied from another source.

Oxygen should be added to the gaseous mixture in an amount about to 200% in excess on a molar basis of that stoichiometrically necessary to react with the S0 and form S0 The gas is then cooled and the S0 absorbed with concentrated sulfuric acid, usually to a temperature less than 300 C. to form fuming sulfuric acid (oleum) having an S concentration of greater than 6%. This is diluted with water or weak acid to form about 6% fuming sulfuric acid (oleum), and this 6% fuming sulfuric acid is used to react with acetone cyanohydrin and alcohol with the formation of methyl methacrylate and ammonium sulfate.

After the S0 is absorbed from the gas, the remainder of the gas is vented.

In the following examples which illustrate the invention, all parts and percentages are by weight unless otherwise specified.

EXAMPLE I 400 parts acetone cyanohydrin was slowly added to 610 parts of 6% oleum. The temperature was allowed to rise to 100 C. After the addition was completed, the mixture was heated to 115 C. for an hour. 10 parts tannic acid were then added to inhibit polymerization. 320 parts methanol and 170 parts water were then added to the mixture, and the mixture was heated to 100 C.; the vapor produced was fractionated to separate and recover methyl methacrylate and methanol. After the vapor ceased to contain appreciable amounts of methyl methacrylate, the residue was removed, diluted with sufficient water to prevent crystallization, and analyzed. The residue, after dilution, contained 36.8% H 50 29.0% water, 24.2% (NH SO 8.5% C H O(NH SO and 1.5% organics having the empirical formula C H O (The method of analysis was such that NH HSO was measured as partly H 80 and partly (NH SO This diluted residue was then introduced into a gas fired burner at the base of the flame and sprayed upward at a rate of 12.0 cc./minute under 150 lbs./in. pressure with natural gas at a rate of 1250 cc./minute and air at a rate of 17,000 cc./minute.

The effluent gas was then cooled to 32 C. and scrubbed to remove water, undecomposed sulfuric acid, and ash, and the resulting gas had the following analysis:

0 mole percent 3.0 S0 do 8.8 CO do 9.1 N, do 79.1 Nitrogen Oxides as N0 parts per million 50 The gas was then heated to 440 C. by passing through heating coils and then passing through a vanadium pentoxide catalytic bed containing a litre of catalyst at a rate of 106,800 cc./minute. The catalyst was preheated to 540 C. by circulation of heated air through the bed. Air was introduced at a rate of 14,760 cc./minute. The resulting gas had the following analysis:

S0 mole percent 0.3 S0 do 6.5 O do 4.5 N do 82.7 CO do 6.5 Nitrogen oxides as N0 parts per million 40 This gas was cooled to 200 C. and then the S0 absorbed with concentrated sulfuric acid by passing the gas at the rate of 97,800 cc./minute through a series of absorption towers packed with graded quartz. The gas had the following analysis on completion of this treatment:

S0 mole percent" 0.3 S0 milligram per cc. 0.001 0 mole percent 4.8 N do 88.0 C0: do 6.9 Nitrogen oxides as N0 parts per million 20% oleum containing small amounts of HNO was recovered. This was diluted with water to form a 6% oleum solution, and this material was recycled for reaction with acetone cyanohydrin.

EXAMPLE II 400 parts acetone cyanohydrin was slowly added to 610 parts of 6% oleum. The temperature was allowed to rise to C. After the addition was completed, the mixture was heated to C. for an hour. 10 parts tannic acid was then added to inhibit polymerization. 320 parts methanol and 180 parts water were then added to the mixture, and the mixture was treated to 100 C.; the vapor produced was fractionated to separate and recover methyl methacrylate and methanol. After the vapor ceased to contain appreciable amounts of methyl methacrylate, the residue was removed, diluted with sufficient water to prevent crystallization, and analyzed. The residue, after dilution, contained 35.8% H 50 30.8% water, 23.5% (NH SO 8.4% C H O(NH SO and 1.5% organics having the empirical formula C H O (The method of analysis was such that NH HSO was measured as partly H 80 and partly (NH SO This diluted residue was then introduced into a gas fired furnace above the burner flame and sprayed downward at a rate of 4360 lb./hr. under a pressure of lbs/in. with natural gas at a rate of 8,700 standard cubic feet/hr. and air at a rate of 150,000 standard cubic feet/hr.

The gas was then cooled to 40 C. and scrubbed to remove water, undecomposed sulfuric acid, and ash. The resulting gas had the following analysis:

S0 mole percent 6.0 CO do 9.9 0 do 3.1 N do 81.0 Nitrogen oxides as N0 parts per million 40 The gas was then heated to 440 C. by passing through heating coils and then passing through a platinum catalytic bed containing 870 Troy ounces of catalyst at a rate of 431,000 cubic feet/hour. The platinum bed was preheated to about 500 C. by circulation of heated air through the bed. Air was introduced at a rate of 33,600 standard cubic feet/hour. The resulting gas had the following analysis:

S0 mole percent 0.2 $0 do 4.9 CO do 8.5 0 do 3.5 N do 82.9 Nitrogen oxides as N0 parts per million 35 This gas was then cooled to 225 C. and the S0 absorbed with concentrated sulfuric acid by passing the gas at the rate of 361,700 cubic feet per hour through a series of porcelain packed absorption towers. The gas had the following analysis on completion of this treatment:

S0 mole percent 0.3 02 dO 3.7 CO do 8.9 N do a 87.1 S0 milligrams/cubic foot 30 Nitrogen oxides as N0 "parts/million 30 20% oleum containing small amounts of HNO was recovered. This was diluted with water to form a 6% oleum solution, and this material was recycled for reaction with acetone cyanohydrin.

I claim:

1. A cyclic process for the production of methyl methacrylate which comprises reacting oleum and methanol with acetone cyanohydrin, thereby forming a mixture containing methyl methacrylate and ammonium sulfate, separating the methyl methacrylate from the rest of the mixture, burning the remainder of the mixture in a flame at a temperature within the range of 850 C.

to 1150 C. to produce a gaseous mixture containing S0 catalytically reacting the gaseous mixture containing S0 with oxygen to form S0 absorbing the 80;, with concentrated H 80 to produce oleum and reacting the oleum with acetone cyanohydrin and methanol to produce a mixture containing methyl methacrylate.

2. A cyclic process for the production of methyl methaerylate which comprises reacting oleum and methanol with acetone cyanohydrin, thereby forming a mixture containing methyl methacrylate and ammonium sulfate, separating methyl methacrylate from the mixture, burning the ammonium sulfate containing portion at a temperature within the range of 850 C. to 1150 C. to form a gas containing sulfur dioxide, oxidizing said sulfur dioxide to form sulfur trioxide by passing the gas containing said sulfur dioxide over an oxidizing catalyst in the presence of oxygen, at a temperature within the range of 400 to 600 C., said oxygen being present in the amount of about 100 to 200% in excess, on a molar basis, of that stoichiometrically necessary to react with sulfur dioxide, absorbing the sulfur trioxide with concentrated sulfuric acid to form fuming sulfuric acid, and reacting the fuming sulfuric acid with acetone cyanohydrin and methanol to produce a mixture containing methylmethacrylate and ammonium sulfate.

3. The process of claim 2 in which the oxidizing catalyst is selected from the group consisting of vanadium and platinum containing catalysts, and in which the concentration of the fuming sulfuric acid reacted with methanol and aceting cyanohydrin is 6% oleum.

4. The process of claim 3 in which the 6% oleum is produced by diluting 20% oleum.

References Cited UNITED STATES PATENTS 3,359,069 12/1967 Furkert et a]. 23-178 2,301,650 11/1942 Titlestad 23-177 2,406,930 9/1946 Titlestad 23-172 2,890,101 6/1959 Borl'el et a1 23119 LORRAINE A. WEINBERGER, Primary Examiner. A. P. HALLUIN, Assistant Examiner.

US. Cl. X.R. 

